Anyone who wanted to push the limits of MS-DOS quickly became familiar with extended memory and expanded memory and the differences between them. They unlocked vast reserves of memory beyond the IBM PC's 640 kilobyte limit. This concern with memory management persisted until Windows 95 and OS/2 arrived.
MS-DOS introduced rudimentary memory management with, I think, version 4.0.
The first Windows version that I seriously tried to use was Windows 386. It included a good memory manager and could do true multi-tasking.
I became fond of Quarterdeck System's Desqview, a text-based windowing multi-tasker that ran atop MS-DOS. It was fast. It took a little work to tune, but with it I could have a word processor, spreadsheet, and database all running simultaneously.
Desqview's memory manager, Qemm with Manifest, was awesome. It seemed to find every last byte of unused memory and put it to use.
During this time there were lots of memory managers available: Qemm, 386 To The Max, etc. The 80386 had allowed access to memory above one megabyte when not in Real Mode, and users were hungry to use that memory.